Chronic osteomyelitis is a persistent and recurring infection of the bone. Unlike an acute infection that develops quickly, the chronic form is a long-lasting condition that can linger for months or even years. This persistence makes the infection challenging to resolve, as the body’s defenses and standard treatments may not be fully effective, complicating its management.
Causes and Risk Factors
An open injury, such as a compound fracture where the bone breaks through the skin, can allow bacteria to directly enter the bone tissue. Infections can also be introduced during surgical procedures, particularly those involving prosthetic materials like plates or screws. An infection from adjacent soft tissue can spread into the bone, or bacteria can travel through the bloodstream from another part of the body to settle in a bone.
The transition from an acute infection to a chronic one involves specific biological processes that protect the invading microorganisms. Over time, the infection can cause bone tissue to die due to a lack of blood supply from inflammation and swelling blocking blood vessels. This dead bone, known as a sequestrum, becomes a haven for bacteria because it is cut off from the body’s immune cells and antibiotics. Bacteria can also form a biofilm, a slimy, protective layer that helps them adhere to bone surfaces and resist treatment.
Certain health conditions and lifestyle factors increase a person’s susceptibility to developing chronic osteomyelitis. Individuals with diabetes are at higher risk, especially with foot ulcers, as are those with peripheral vascular disease, which impairs blood flow to the limbs. A compromised immune system, from a medical condition or medication, also reduces the body’s ability to fight off an initial infection. Smoking is another risk factor, as it slows blood flow and healing.
Recognizing the Symptoms
The signs of chronic osteomyelitis can be subtle and develop slowly over time. A common symptom is a persistent, deep pain in the affected bone, accompanied by tenderness, swelling, and warmth in the overlying area. The skin over the infection might also appear red or discolored, and these symptoms can be mistaken for an injury, particularly in the hip, pelvis, or spine.
In some cases, a draining sinus tract may form, which is a channel that develops from the infected bone to the surface of the skin. This opening can intermittently leak pus, a clear sign of an underlying infection. While systemic symptoms like fever, chills, and general fatigue are common in acute osteomyelitis, they are less pronounced or may be absent in the chronic form. A person might experience a general feeling of being unwell or unexplained weight loss.
The Diagnostic Process
Diagnosing chronic osteomyelitis begins with a thorough physical examination and a detailed review of the patient’s medical history. The doctor will look for signs of tenderness, swelling, and redness and ask about any recent injuries, surgeries, or other infections.
Blood tests are ordered to look for markers of inflammation in the body. Tests such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) can indicate an infection, though they do not confirm it is in the bone. These tests are also useful for monitoring the body’s response to treatment.
Imaging studies are important for visualizing the condition of the bone. X-rays are a common first step and may reveal bone damage, but changes might not be visible in the early stages. A Magnetic Resonance Imaging (MRI) scan is effective at showing the extent of the infection, including any associated soft tissue abscesses. Bone scans can also be used to pinpoint the infection by detecting areas of increased metabolic activity in the bone.
The definitive method for diagnosing chronic osteomyelitis is a bone biopsy. A small sample of the affected bone is surgically removed and sent to a laboratory for analysis. This test confirms the presence of an infection and identifies the specific type of bacteria or fungus causing it. This information is important for selecting the most effective antibiotic for treatment.
Approaches to Treatment
Medical treatment almost always involves a long course of antibiotic therapy. This treatment begins with intravenous (IV) antibiotics administered in a hospital setting to ensure high concentrations of the medication reach the infected bone. After an initial period, this may transition to oral antibiotics, which must be taken for several weeks or even months to fully clear the infection.
Surgical intervention is frequently necessary. The primary procedure is debridement, where a surgeon removes all infected and dead bone tissue (sequestrum). Removing this non-viable tissue is a necessary step because it eliminates reservoirs where bacteria can hide from antibiotics and the immune system. For this reason, antibiotic therapy alone is often insufficient to cure the infection.
Other surgical techniques may be employed to promote healing and restore bone function. After infected tissue is removed, surgeons can fill the resulting void with bone grafts from the patient’s body or a donor to help regenerate new bone tissue. In severe cases where the infection cannot be controlled and the limb is no longer functional, amputation may be considered to prevent the infection from spreading.
Potential Complications
If not managed effectively, chronic osteomyelitis can lead to several serious complications. The persistent infection weakens the bone, making it susceptible to pathological fractures, where it can break under normal stress. The infection can also lead to abscesses, which are pockets of pus in the bone or surrounding soft tissues. A significant risk is the spread of infection to the bloodstream, a condition known as sepsis, which is a life-threatening inflammatory response. In rare instances, a long-standing draining sinus tract can lead to the development of squamous cell carcinoma, a type of skin cancer, within the tract.